140 MODERN CLASSIFICATION OF INSECTS. 
sheaths varies greatly in length in the different species; but the 
articulation always takes place near the extremity of the body: when 
at rest, these two demi sheaths (which are externally convex and 
pilose, but internally concave and polished) are brought into con- 
tact, and enclose between them the terebra or borer itself, which 
is a compound instrument formed (like the borer of Urocerus) of 
three parts, the superior (c) being nearly cylindrical, and channelled 
beneath for the reception of the two* slender, rigid, filamentous 
spiculz (ce, c), with membranous edges transversely striated at the ex- 
tremity (fig. 75. 12.); the union of these three pieces forms a central 
passage (as in jig. 13. being a section of the borer itself, with the two 
spicule in situ) for the protrusion of the egg. Jig. 75. 9. represents 
the under side of the abdomen, with the different parts similarly 
lettered. Fig. 75. 10. exhibits a more highly magnified view of the 
base of the ovipositor, showing that (c) the superior channel of the 
terebra originates from the base of the basal part (b) of the outer 
sheath ; and fig. 75. 11. represents the same parts beneath, c being the 
deflexed sides of the superior canal of the terebra, and e, c, the base 
of the two spicule. 

* De Geer, Latreille, and Burmeister incorrectly describe the central terebra 
as composed of only two, instead of three, parts; the latter further endeavouring 
to refer this incorrectly regarded structure to that of Sirex (loc. cit. supra). 
Gravenhorst even regards the central terebra as not being a composite instrument. 
Réaumur has given numerous figures of the female of a species of Pimpla engaged 
in oviposition (in which the terebra is not represented as disengaged from its 
sheaths), and of the details of the ovipositor, but in a very rude manner. His 
fig. 10. pl. 29. tom. vi. represents the two rows of serrations at the extremity of 
the terebra “entre lesquelles une membrane blanche est sensible,” besides which 
there is an elongated slender “ corps blane, que j’ai fait sortir du bout de Ja tarriére 
par la pression.” This latter must, I should presume, be membrane rather than a 
distinct organ. 
